Bricks are produced from clay, finely pulverized shale or a mixture thereof, by extruding the raw material, shaping the extruded raw material and firing the shaped body. In certain areas, the raw material for producing the brick contains more than 50% shale (the remainder being clay). Because of the relatively small percentage of clay used in the brick, there is a lack of plasticity and a lack of green strength which causes a great many failures during the production process and after firing. Additionally, the lack of green strength and/or plasticity in the freshly extruded brick containing appreciable amounts of shale, causes in many cases, a deformity which results in an inferior brick which can only be sold at a significantly reduced price if it can be sold at all.
It is known that the addition of sodium bentonite to clay, in the manufacture of brick, will increase the plasticity; however, in those bricks containing more than 50% by weight of shale the addition of sodium bentonite does not appreciably aid in increasing the plasticity and green strength of bricks formed from this shale and therefore sodium bentonite is of little or no value in decreasing the number of rejects and increasing the green strength and/or plasticity of brick compositions containing relatively large amounts of shale, and particularly hard or petrified shale.